1. Field of the Invention
The present invention relates to a spindle motor and a hard disk drive including the same.
2. Description of the Related Art
In general, a small-sized spindle motor used in a hard disk drive (HDD) serves to rotate a disk so that a magnetic head may read data stored thereon or write data thereto.
In addition, the small-sized spindle motor includes a fluid dynamic bearing assembly, a bearing clearance provided in the fluid dynamic bearing assembly being filled with a lubricating fluid.
In addition, at the time of rotation of a shaft, the lubricating fluid filling the bearing clearance is pumped to form fluid dynamic pressure therein, thereby rotatably supporting the shaft.
However, pressure lower than atmospheric pressure, that is, negative pressure, may be generated in the bearing clearance by the pumping of the lubricating fluid at the time of rotation of the shaft.
In this case, air contained in the lubricating fluid may expand to form air bubbles. When these air bubbles are introduced into a groove pumping the lubricating fluid, sufficient fluid dynamic pressure may not be generated, and vibrations may be generated, such that the introduced air bubbles may deteriorate rotational characteristics.
Therefore, a circulation hole for reducing the generation of the negative pressure is formed in a sleeve, and the generation of negative pressure may be suppressed by the circulation hole.
A configuration in which a circulation hole for reducing the generation of negative pressure is formed to be inclined and to connect a bearing clearance formed by a sleeve and a cover member and a bearing clearance formed by a liquid-vapor interface to each other is disclosed in US Patent Laid-Open Publication No. 2009-0080819 (Related Art Document).
However, it may be difficult to process the circulation hole, and at the time of processing the circulation hole, a defect of the sleeve may be generated.